Mat of inorganic oxide fibers,its method of preparation and its impregnation with catalytic materials

ABSTRACT

1. AN ANNULAR FORM LIQUID PERVIOUS MAT OF FIBROUS MATERAIL THAT IS SUITABLE FOR THE CONTACT OF A FLUID FLOW THERETHROUGH, WHICH COMPRISES, A PLURALITY OF RECROSSING HELICALLY WOUND LAYERS OF LONG, FLEXIBLE, POROUS HIGH SURFACE AREA REFRACTORY INORGANIC OXIDE FIBER, WITH SAID FIBER HAVING BEEN PREPARED BY FORMING A NON-HOLLOW FIBER FROM A MIXTURE OF A REFRACTORY INORGANIC OXIDE SOL AND A FIBERFORMING ORGANIC POLYMER AND BY SUBSEQUENTLY CALCINING THE FIBER AT A TEMPERATURE OF FROM ABOUT 300 TO ABOUT 1000* C. TO BURN OFF THE FIBER-FORMING ORGANIC POLYMER PORTION OF THE COMPOSITE.

Ot. 22, 1974 .1.550551 f 3,843,561 uur op moRGANIC oxrmal nanas, I'rsMETHOD oF PREPARATION mn v `I'rs IMPREGNATION WITH cA'rALYTIc MATERIALSv Filed Aug. 22, 1972 u l ll l United States Patent O "Ice U.S. Cl.252-465 Claims ABSTRACT OF THE DISCLOSURE A preformed mat of fibrousmaterial and the method for preparing the same. Also included is a fluidcontacting chamber utilizing a particular form of the mat of fibrousmaterial. The mat comprises a fibrous, flexible, porous, refractoryinorganic oxide material which is wound onto a mandrel in a plurality oflayers to form a resulting annularly shaped form. The mat is capable ofbeing utilized as filtering media, adsorption-absorption media,catalyst, and/or catalyst support.

This application is a continuation-in-part of a copending application,Ser. No. 36,732, filed May 13, 1970, and now abandoned.

SPECIFICATION The present invention relates to a mat of fibrous materialand the method of preparation. More specifically, the invention isdirected to a mat formed of long fibrous, flexible, porous, refractoryinorganic oxide material for utilization in the contacting of a fluidflow and to the method of preparing the mat. It is also directed to aparticular type of fluid contacting chamber utilizing one form of theresulting mat.

The use of materials of various types, configurations and substancessuitable for contacting lfluid streams, is generally well known in bothconsumer and industrial applications. Examples are: filtrationapplications, wherein fibers of various sorts are used to filter outsolid particulates in a fluid stream; catalytic reaction applicationswherein materials of particulate form are utilized as a catalyst supportor catalyst for varous types of catalytic reactions in refineries, etc.;or in different sieve applications wherein materials of various formsare utilized to separate or adsorb components of fluid streams. However,it is believed that the particular form of the preformed mat disclosedherein, the method of preparing the mat, the particular fluid contactingchamber, as well as the preferred materials for forming said mat is anovel concept. t

Thus, it is a principal object of this present invention to provide fora special form of mat of fibrous material suitable for contacting afluid flow.

It is also an object of this invention to provide a method of preparinga special form of mat from long fibrous material suitable for contactinga fluid flow.

More particularly, it is an object of this present invention to providea mat of fibrous material suitable for contacting a fluid flow and themethod of preparing the same, the mat of fibrous material beingstructured from a fibrous, flexible, porous, refractory inorganic oxidematerial of long staple form.

Still another object of this invention is to provide for a mat offibrous material suitable for contacting a uid flow and the method ofpreparing the same, the mat of material being suitable for catalyticreactor utilization and being structured from a flexible, fibrous,porous refractory inorganic oxide material of long staple form.

Still another object of this present invention is to provide a mat offibrous material of an annularly shaped form and the method of preparingthe same.

Another object of this present invention is to provide for a fluidcontacting chamber utilizing an annularly shaped mat of fibrousmaterial, the fluid contact material being structured from a fibrousmaterial of long staple form that has been wound to have a plurality ofrecrossing layers.

In one of its broadest aspects, the present invention provides for atubular mat of fibrous material suitable for contacting a fluid flow,which comprises a plurality of layers of fibrous, flexible, porous,refractory inorganic oxide material, each layer comprising a long fiberWound helically into a tubular form. In this resulting annularly shapedform, the mat may be cut to form a flat mat or may be utilized in anannularly shaped chamber or section of a chamber. By referring to theform of each layer as tubular, it is meant to encompass other thancircular cross-sections, such as oval and the like.

Also considered as a part of this invention is a method for preparing amat of fibrous material suitable for contacting a lfluid flow. Themethod comprises helically winding a plurality of layers of fiber of along flexible, porous, refractory inorganic oxide configuration onto amandrel to form a resulting annularly shaped mat.

A preferred source of fibers for utilization in conjunction with thepresent invention is a method which comprises mixing a refractoryinorganic oxide sol with a fiber-forming organic polymer; drawing orspinning fibers from the mixture; and consequently burning off theorganic ingredient and calcining the fiber to a flexible, porousstructure. The resulting inorganic refractory oxide fibers are capableof being utilized as a filtering media, an adsorption-absorption media,a catalyst, and/or a catalyst support.

The refractory inorganic sol utilized in accordance with the method setforth heretofore includes hydrous sols, for example, an alumina sol,chromia sol, zirconia sol, silica sol, thoria sol, and the like, as wellas combinations thereof, such as alumina-chromia sols, alumina-zirconiasols, etc., to form the corresponding refractory inorganic oxide fibers.Said sols include those sols resulting from hydrolysis andconcentrations of aqueous solutions of one or more appropriate salts,such as zirconium acetate, whereby a colloidal dispersion, stable in theremaining liquid, is formed. For purposes of illustration, the methodwill be described with reference to the preparation of alumina fibersbut with the understanding that the method is also applicable to thepreparation of fibers comprising other inorganic oxides or combinationsthereof. The alumina sols herein contemplated can be prepared by thehydrolysis of a suitable acid salt of aluminum such as aluminumchloride, aluminum sulfate, aluminum nitrate, aluminum acetate, etc., inaqueous solution, and treating said solution at conditions to form anacid anion deficient solution or sol. Reduction in the concentration ofacidic anion formed by the hydrolysis reaction may be accomplished inany conventional or otherwise convenient manner. Thus, the acid anionconcentration can be reduced by utilizing aluminum metal as aneutralizing agent. In this case, the salt of neutralization is analuminum salt subject to hydrolysis in the ultimate sol formulation. Insome cases, as in the ,case of aluminum acetate, when the acid anion issufficiently volatile, the desired acid anion deficient solution or solmay be prepared simply by heating. Another method of producing asuitable alumina sol is in the electrolysis of an aluminum saltsolution, such as an aqueous aluminum chloride solution, in anelectrolytic cell having a porous partition between anode and cathodewhereby an anion deficient aluminum salt solution, or sol, is recoveredfrom the cathode compartment.

Preferably, the sol is an aluminum chloride sol prepared, for example,by digesting aluminum pellets or slugs in aqueous hydrochloric acidand/or aluminum chloride solution-usually at about reflux temperature.Aluminum chloride solutions are preferably prepared to contain aluminumin from about a 1:1 to about a 2:1 atomic ratio with the chloride anion.

Alumina or other refractory inorganic oxide sols are capable of beingformed into a tacky, viscous material which may be drawn into fibers orfine filaments, as set forth in U.S. Pat. 3,614,809 and 3,632,709.However, diiculty has been found in making or spinning such fibers orfilaments into extended lengths as would be suitable to Wind on a spooland then unwind to form layers around a mandrel and, as a result, it ispreferable to include a fiberforming organic polymer with the sol asheretofore noted.

The selected fiber-forming organic polymer must be substantially stableat fiberizing conditions. The soluble, liber-forming, organic polymersas contemplated herein include the modified natural products prepared aswater soluble derivatives of natural occurring, fiber-forming, organicpolymers or resins, Thus, the soluble, fiber-forming, organic polymerscan be a starch derivative such as starch acetate, starch ether, anionstarches, etc., or a soluble cellulose derivative, for example, thealkyl and hydroxy 'alkyl cellulose derivatives like methylcelluose,ethylcellulose, ethylmethylcellulose, hydroxyethylcellulose,hydroxyethylmethylcellulose, hydroxypropylmethylcellulose,ethylhydroxymethylcellulose, etc., and also watersoluble derivativessuch as carboxymethylcellulose, carboxymethylhydroxyethylcellulose, andthe like. Preferably, the soluble, fiber-forming, organic polymer is asynthetic product such as soluble polyalcohols, polyacids, polyamines,polyethers, and polyamides, derived from the variety of syntheticmonomers. Suitable synthetic organic polymers include the solublepolyvinylalcohols, polyurethanes, polyacrylic acid salts,polyacrylamides, polyvinylmethyl ethers, polyvinylpyrrolidones,polyethylene oxides, and the like. A selected organic polymer must alsobe substantially stable at fiberizing conditions, i.e., in thetemperature range of from about 5 to about 90 C. Also, suitably, theorganic polymer may comprise from about 0.5 to about wt. percent of thereaction mixture, although larger amounts could be used. Since theorganic polymer is expended in the liber making process, it is desirable'to utilize a minimum amount commensurate with a desired product fiberquality.

Actually, the inclusion of a soluble fiber-forming, organic polymer inthe sol imparts an added cohesiveness thereto which enables the sol tobe drawn or stretched into longer, finer fibers or filaments of anorderly molecular arrangement or orientation before the sol sets to agel. The end result is upon subsequent calcination, a refractoryinorganic oxide liber of improved strength and tiexibility.

The reaction mixture thus prepared is concentrated to a tackyconsistency while maintaining a substantially liquid phase. The reactionmixture is suitably reduced to the desired consistency by theevaporation of water therefrom, suitably by simple evaporation uponstanding or upon stirring in an open vessel, but more conveniently bytreating in a vacuum evaporator at ambient temperature, a tackyconsistency being achieved at a viscosity of from 'about l to about20,000 poise. The further evaporation of water and initial gelaton ofthe sol is effected as the concentrated reaction mixture is being drawninto stable fibers in an atmosphere of controlled temperature andhumidity.

Fiberizing conditions relate principally to the temperature and humidityof the environment in which the fibers are formed. The relatively largesurface area presented by the fibers in the process of being formedpermits a relatively rapid evaporation of moisture therefrom with theformation of a stable librous hydrogel, provided that the moisturecontent of the environment is sufliciently low. If, however, themoisture is too high, the desired rapid evaporation does not occur andthe fibrous hydrosol may in effect absorb sufficient moisture tolcollapse in a formless mass. The iiberizing environment should comprisea relative humidity of less than about and preferably from about 10% forextrusion spinning. The temperature of the iberizing environment issomewhat less critical and may be from about 5 to about 90 C., andpreferably from about 25 to about 90 C. The described reaction mixturemay be procesed or formed into fibers by a slow and constant injectionof the concentrated reaction mixture into the atmosphere of controlledhumidity and temperature, drawing the injected mixture into iibers andsubjcting the fibers thus formed to a specific heat treatment to yield aporous, flexible product. The reaction mixture may be extruded or passedthrough a perforated plate comprising one or more relatively largeorifice openings, the resulting fibers being rapidly attenuated usingthe material being extruded or pulled through the perforated plate as aconstant feed. In any case, the reaction mixture is preferably drawn orextruded into fibers with a maximum diameter of less than about 20microns for improved flexibility.

The fibers thus formed are thereafter calcined at a temperature of atleast about 300 C., and preferably from about 300 C. to about l000 C.,in an air atmosphere, whereby the organic matter is burned from thefibers and a -iiexible refractory inorganic oxide product is recovered.As will be apparent with reference to the appended examples, theincorporation of a soluble, fiber-forming, organic polymer in `the solsubsequently processed intoiibers, results in a yield of porous,iiexible fibers.

In summary, one preferred embodiment of making the fiber for the presentinvention relates to a method of preparing alumina fibers whichcomprises preparing an alumina sol by effecting a reduction in thechloride anion concentration of an aqueous aluminum chloride solution,said sol containing from about 12 to about 14 wt. percent aluminum infrom about a 1:1 to about a 2:1 atom ratio with the chloride contentthereof; admixing a soluble polyethylene oxide polymer therewith andforming a substantially liquid phase mixture, said polymer comprisingfrom about 0.5 to about 25 -wt. percent of said mixture; concentratingthe mixture to a viscosity of from about 1 to about 20,000 poise; andthereafter drawing the concentrated mixture into fibers in an atmospherecharacterized by a relative humidity of from about 30% to about I60% anda temperature of from about 25 to about 90 C., and calcining theresulting fibers .in air at a temperature of from about 300 to aboutl000 C.

The following examples are presented in illustration of the method formaking the desired form of liexible liber of this invention and are notintended as an undue limitation of the generally broad scope of the.invention as set out in the appended claims.

EXAMPLE I An alumina sol was prepared by digesting an excess of aluminummetal in laqueous hydrochloric acid under reflux conditions (98-l15 C.).The sol analyzed 12.49% aluminum, 10.75% chloride and had a specificgravity of 1.3630. To 67.0 grams of the sol was added, with stirring, 80grams of a 5 wt. percent aqueous polyurethane solution. The reactionmixture was concentrated by the evaporation of water therefrom whilemaintaining substantially liquid phase conditions. The concentratedreaction mixture was drawn into fibers in an atmosphere characterized bya relative humidity of 45-55% and a temperature of S20-30 C. The organicmatter was burned from the fibers and the fibers calcined for about 1hour at a temperature of 550 C. in air. The mean diameter of thecalcined fibers was about 4 microns. Measurement of surface areaproperties by nitrogen absorption indicated a surface area of 100m.2/gm., a pore volume of 0.14

cc./gm. and a pore diameter of 56 A. The fibers were very flexible andresilient.

EXAMPLE II A chromia-alumina sol was prepared by digesting aluminummetal in aqueous chromium chloride solution. The sol analyzed 10.02%aluminum, 2.87% chromium and 10.14% chloride. The specific gravity ofthe sol was 1.349. To 118.7 grams of the sol was added, with stirring,6.2 grams of polyvinylpyrrolidone having an average molecular weight ofabout 40,000. The reaction mixture was concentrated by the evaporationof water therefrom while maintaining substantially liquid phaseconditions. The concentrated reaction mixture was drawn into fibers inan atmosphere characterized by a relative humidity of 45-5 5% at atemperature of 20-30 C. The organic matter was burned from the fibersand the fibers calcined at a temperature of about 550 C. in air. Themean diameter of the calcined fibers measured 6 microns. Measurement ofsurface properties by nitrogen absorption indicated a surface area of327 m.2/gm., a pore volume of 0.23 cc./ gm. and a pore diameter of 28 A.The fibers were very fiexible and resilient.

As a catalyst support, the resulting inorganic refractory oxide fibersmay be impregnated with a catalytic active metal or metallic oxide. Ofparticular interest are those catalysts comprising one or more metals ofGroup IB, V, VI, VII, VIII, including molybdenum, tungsten, chromium,palladium, copper, nickel, platinum, iron, cobalt, ruthenium, rhodium,osmium, and iridium. Regardless of the particular refractory materialsemployed and regardless of the particular method selected forpreparation of such a support, the catalytically active metalliccomponent may be added to the inorganic refractory oxide in anysuitable, convenient manner.

The present invention also provides for a uid contacting chamberincluding a mat of fibrous material, said mat comprising a plurality oflayers of fibers of a flexible porous inorganic refractory configurationhelically wound around a tubular-form screen having perforationstherein, the interior of said tubular-form screen section establishing afiuid distribution manifold for said contact material and theperforations therein establishing communication from said distributionmanifold to said fibrous material.

The mat of fibrous material, the method for preparing the same, and thechamber in which such a mat may be used, as well as other advantageousfeatures in connection therewith, are better set forth and explained byreference to the accompanying diagrammatic drawing and the followingdescription thereof.

FIG. l is a schematical representation of a method for preparing theannular-shaped mat of fibrous material.

FIG. 2 is a sectional view of an embodiment of a contact chamberutilizing a mat similar to the mat of FIG. 1.

Referring now more particularly to FIG. 1 of the drawing, there is shownschematically an apparatus that may be utilized in winding a mat offibrous material. Shown is a reel or spool means 1 which has been woundwith a fiber or yarn of a flexible, porous, refractory inorganic oxideconfiguration 2 that has been prepared by a suitable method for making along flexible filament. It may be a fiber of catalyst form, or a fiberthat is suitable for the support of a catalytic component, or a fiberwhich has already been impregnated with that catalyst. For purposes ofillustration, the means for supporting the spool is not shown, but maybe by conventional manner. The spool itself may be caused to rotate bypower means also not shown, but on the other hand,-may be provided witha tension clutch to maintain proper tension in the fiber or yarn as itis being wound. The fiber or yarn 2 is threaded through a torus 3 orother form of guide means which is supported by suitable means notshown, which will be powered to move back and forth at a programmed ratein the directions 4 and 5. Also included in this apparatus is a motor 6having a shaft to which a pulley 7 is connected. Pulley 7 communicateswith a pulley 8 via a belt 9 which in turn is connected to a shaft 10which is supported by posts 11 and 12 in a manner which allows it torotate within the confines of the posts 11 and 12. To the shaft amandrel 20 is connected on which the fiber or yarn 2 is to be wound.Mandrel 20 may be a permanent type mandrel used only as a form on whichthe fiber 2 is wound, or, on the other hand, it may be perforated andthus serve as a tubular-form perforate screen for a contact chamber inwhich it may be utilized, which is the case in FIG. l since perforationsare shown in the drawing. Since the tubular-form screen section ormandrel 20 is hollow, it is supported via a cylinder 26 which isconnected to the shaft 10. To remove the resulting annularly shaped matfrom the apparatus, the left-hand portion of the shaft 10 may beprovided with a removable connector 27, and support post 12 may beprovided with a provision so that it may be swung away from shaft 10.Thus, after winding the fiber or yarn 2 onto the removable mandrel, themandrel may be removed by disconnecting connector 27 and swinging post12 clear of shaft 10. Of course, the apparatus of FIG. 1 is presented byway of example, and other apparatus of more complex nature may beprovided for carrying out the method of this invention.

The mat is formed by helically winding a plurality of layers of thefiber 2 onto the mandrel to form the resulting mat 30. This isaccomplished by turning the shaft 10 via motor 6 at a programmed rate ofspeed and moving the guide means 3 at a programmed rate inthe twodirections 4 and 5. To maintain the fiber or yarn at a constanttautness, a tension clutch may be provided in the supporting means ofreel 1. Thus, as the guide means 3 moves longitudinally across themandrel 20, a layer of a fiber is wound helically into a tubular form.The resulting mat comprises a plurality of layers of the fibrousmaterial. The density of the resulting mat may be controlled bycontrolling the helical angle or pitch distance between revolutions ofthe fiber. A more dense mat will be formed by winding the fiber througha smaller helical angle. The particular method enables one to form auniformly dense mat with a substantial control of the density. For somepurposes and some fibrous materials, a setting agent may be utilized inconjunction with the fiber to aid in forming a coherent mat of material.The resulting mat 30 with the screen 20 or without the screen may thenbe cut and flattened out to form a relatively fiat-shaped mat of fibrousmaterial, or, on the other hand, it may be used in its present form,that being an annularly shaped form. Of course, if the mandrel is notneeded for the finished product, it may form a permanent part of theapparatus.

Referring now more particularly to lFIG. 2 of the drawing, there isshown a fluid contacting chamber which may be a catalytic reactor andwhich includes a mat of fibrous material 30. Mat 30' comprises aplurality of layers of fibrous, flexible, porous, refractory inorganicoxide material which have been helically wound around a tubularformscreen 20 having perforations 25 thereon. Thus, it is seen that mat 30is a proportional modification of the annular mat of FIG. 1 whichincludes the screen or mandrel 20. The interior 40 of the tubular-formscreen 20 establishes a fluid distribution manifold for the contactmaterial and the perforations 25 establish communication from thedistribution manifold to the fibrous contact material 30. Also includedin this particular contact chamber is a tubular-form outer housing 41which has an end closure means 42 with a port means 43 and a removableend closure means 44 with a port means 45 communicating with a manifoldsection or the interior 40 of screen 20. A large tubular-form perforatescreen 50 with perforations 51 therein is connected to the outer housing41 via end plates 52. Screen section 50 is also of a tubular form andhas an end closure means 53.

Tubular-form screen section 50 is spaced from the outer housing 41 toform a distribution manifold 55 communicating with the brous contactingmaterial via the perforations 51. It is contemplated that for certainapplications screen 50 be omitted from the fluid contacting chamber.

The mat 30' with the perforated screen 20' was inserted into the spacedefined by the interior of screen 50 and subsequently the end closuremeans 44 was placed and sealed onto the outer housing 41 to form theresulting fluid contacting chamber. Thus, it is seen that a fluidcontacting chamber utilizing the annular-shaped mat formed by the methodas set forth hereinbefore is fabricated in a relatively uncomplicatedmanner. Actually, the mat of fibrous material is a cartridge whenutilized in the chamber of FIG. 2. If used for a filter or reactorapplication, after the brous material becomes contaminated or useless insome Way, end portion 44 could be removed, and the fibrous mat withscreen could be replaced.

f course, the chamber as shown in FIG. 2 is a schematical representationand all the details of construction are not shown. For example, tofacilitate the seal and attachment of end section 44 to the chamber,bolts or other forms of fastening means would be needed. Actually, thechamber is ideally suited for catalyst reactions. That is, the brousinorganic oxide material may serve as a catalyst or a catalyst supportmaterial having a catalyst impregnated thereon.

It is to be noted that the specilic examples herein shown and describedare illustrative only and any variations in structure, proportions, andmember thickness should be considered to form part of this inventioninasfar as they fall within the spirit and scope of the claims.

I claim as my invention:

1. An annular form fluid pervious mat of fibrous material that issuitable for the contact of a fluid flow therethrough, which comprises,a plurality of recrossing helically wound layers of long, flexible,porous high surface area refractory inorganic oxide ber, with said fiberhaving been prepared by forming a non-hollow fiber from a mixture of arefractory inorganic oxide sol and a fiberforming organic polymer and bysubsequently calcinng the ber at a temperature of from about 300 toabout 1000 C. to burn otr' the fiber-forming organic polymer portion ofthe composite.

2. The mat of Claim 1 further characterized in that said inorganic oxidesol is an alumina.

3. The mat of Claim 1 further characterized in that said inorganic oxidesol is chromia-alumina. f

4. The mat of Claim 1 further characterized in that said ber isimpregnated with a catalytically active metal or metal oxide.

5. The mat of Claim 1 further characterized in that said catalyticimpregnation is with platinum.

6. A method of preparing a uid pervious mat of brous material forcontacting a uid flow which comprises the steps of:

(a) drawing long flexible fibers from a mixture of a refractoryinorganic oxide sol and a fiber-forming organic polymer at fiberizingconditions;

(b) calcining the resulting drawn fibers at a temperature of from about300 to about 1000 C. whereby the fiber forming organic polymer is burnedoil the fiber to form a resulting flexible, porous, refractory inorganicoxide fiber; and

(c) helically winding said resulting ber back and forth over a mandrelto provide a plurality of recrossing layers and to form a resultingannularly shaped mat.

7. The method of Claim 6 further characterized in that said inorganicoxide sol is alumina.

8. The method of Claim 6 further characterized in that said inorganicoxide sol is chromia-alumina.

9. The method of Claim 6 further characterized in that said fiber isimpregnated with a catalytically active metal or metal oxide.

10. The method of Claim 9 further characterized in that saidimpregnating is with platinum.

References Cited UNITED STATES PATENTS 3,697,447 10/ 1972 Bettinardi252-477 R 3,614,809 10/1971 Hayes et al. 65-11 R 3,632,709 1/ 1972 Hayeset al 106-65 X 3,529,044 9/ 1970 Santangelo 23-202 X 3,560,408 2/ 1971Kiehl et al 423-214 X 3,663,182 5/ 1972 Hamling 423-263 X DANIEL E.WYMAN, Primary Examiner W. I. SHINE, Assistant Examiner U.S. Cl. X.R.

252-463, 466 PT, 477 R; 423-2132, 213.5; 23-288 F; -520, 523, 527;ZID-497.1

1. AN ANNULAR FORM LIQUID PERVIOUS MAT OF FIBROUS MATERAIL THAT ISSUITABLE FOR THE CONTACT OF A FLUID FLOW THERETHROUGH, WHICH COMPRISES,A PLURALITY OF RECROSSING HELICALLY WOUND LAYERS OF LONG, FLEXIBLE,POROUS HIGH SURFACE AREA REFRACTORY INORGANIC OXIDE FIBER, WITH SAIDFIBER HAVING BEEN PREPARED BY FORMING A NON-HOLLOW FIBER FROM A MIXTUREOF A REFRACTORY INORGANIC OXIDE SOL AND A FIBERFORMING ORGANIC POLYMERAND BY SUBSEQUENTLY CALCINING THE FIBER AT A TEMPERATURE OF FROM ABOUT300 TO ABOUT 1000* C. TO BURN OFF THE FIBER-FORMING ORGANIC POLYMERPORTION OF THE COMPOSITE.